BRAW recommends using nest boxes that have proven to be highly attractive to bluebirds. These boxes are shallow (4-5” from bottom of hole to nesting platform), narrow (4” x 4” nesting platforms), have oval openings (1 3/8” x 2 ¼”) and are unvented (vents can be opened after June 1 in areas where black flies are not prevalent). Any box that meets these specifications is recommended by BRAW.
The two most productive boxes recorded by BRAW are:
PVC Nest Box by Pat Ready
The PVC nest box is nothing new for Bluebirders. Steve Gilbertson of MN designed his many years ago and found it very successful for attracting bluebirds but not the invasive House Sparrow. I’m not copying his design in the least. This is a design I came up with using minimal materials and easy enough to make. Use a mirror for monitoring or as I do I use my iPhone and tip it in the entrance hole for a peak & a pic.
DISCLAIMER: This PVC box is not endorsed by BRAW.